As a matter of interest, which brand and model # of router do you use?
Most routers have a fairly straight forward interface to configure the forwarding of incoming ports, so if I can get hold of the brand and model # of your router, I may be able to guide you through how to configure its NAT to map incoming connections.
If you would like to try yourself:
First you need to get your PC’s IP address. A simply way to do this is to click start -> Run, type in “cmd” into the ‘Open:’ field and click ‘OK’. Type “ipconfig” into the black command prompt window that appears and press enter. In the information displayed, look for 'IP Address . . . '. The group of digits separated with dots on this line is your PC’s IP address. The default Gateway IP address is the IP address of your router as well as its web interface. You can close the command prompt window by either clicking the ‘X’ or typing in “exit” and pressing enter.
To access your router’s web interface, bring up a browser Window and type in 'http://(Gateway IP address)" and press enter. For example if your Gateway IP address is 192.168.0.1, type in “http://192.168.0.1/” into the address field and press enter to bring up the Router’s web interface. While a few routers such as some Netopia models don’t ask for a password, the majority of them require at least their default username and password to get in. If you don’t have your user manual handy, browse to the following site to see if it lists the default login details for your router:
Once in, look for a NAT, Virtual Server or Firewall section. For D-Link routers which have both Virtual Server and Firewall menu’s, go into the Virtual Server menu. Then set up a new rule to allow an incoming connection with the TCP port range of 6881 to 6889 to your PC’s IP address and save this rule. If all goes well, your BitTorrent client should be able to start accept incoming connections.